Dual thermoelectric cooler optoelectronic package and manufacture process

ABSTRACT

A twin-Thermoelectric cooler design including two independent thermoelectric coolers sharing the same base (hot side ceramic plate). People familiar with the art understand that the number of independent TEC sharing the same base is not limited to two. Depending on application needs any number of TECs can be constructed on the same base and be controlled independently.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to microelectronic and optoelectronicpackaging. More particularly the present invention relates to anintegrated dual thermoelectric cooler and a method of manufacture.

[0003] 2. Brief Description of the Related Art

[0004] A thermoelectric cooler (TEC), or Peltier cooler has been widelyused in optoelectronic and microelectronic industries for many years.TEC maintains devices such as laser, CCD, and microprocessor attemperatures at which the devices perform the best. When multipledevices are assembled in one enclosure, especially when opticalalignment among the devices is critical, however, packaging design andprocessing become complicated.

[0005] Maintaining a device at its best performing temperature, whilebeing able to vary temperatures of other devices is a key application ofthe current invention. A thermoelectric cooler functions based upon thePeltier effect—a phenomenon discovered in early 19^(th) century that,accompanying electric current flow through conductors, heat flows in thedirection of charge carriers. As depicted in FIG. 1, the electric-flowinduced thermal flow is more pronounced in circuits containing DC powersupply and dissimilar conductors as shown in FIG. 1. In n-typeconductors, electrons are charge carriers flowing from negative pole ofDC power supply through conductors A and B to the positive pole. Heatflows from the bottom of conductor B to its top, hence the term heatpump. In p-type conductor, holes are charge carriers; holes and heatflow from the end linked to positive pole of power supply to the endthat is connected to the negative pole.

[0006] In circuits that contain both n- and p-type conductors in series,electrons and holes flow in opposite directions, as shown in FIG. 2.Heat flows from the bottom to the top in both B and C conductorsresulting in constructive heating and cooling effect. When many of thesethermal couples are assembled together in series electrically and inparallel thermally; the product, thermoelectric cooler, has enoughheating and cooling power for engineering applications.

[0007] TECs typically require 3 to 10 V and 1 to 2 A DC power to achieve60 to 80° C. ΔT cooling. ΔT, temperature differential between cold andhot side of TE cooler, is a measure of the cooling power of TEC.

[0008] Space is at a premium in optoelectronic packaging. As such, whatis needed in the art is a TEC that takes up a minimum of space, that canprovide multiple controls along its length, and is easily manufacturedand maintained.

[0009] Thus, what is needed in the art is a multiple-TEC concept thatencompasses TEC design, manufacturing, and applications. This conceptsimplifies multiple-TEC design and manufacturing process; it alsoenhances optoelectronic device packaging process flexibility.Additionally, the overall component assembly time and cost are reduced,and the quality and reliability of the component assembly is increased.

SUMMARY

[0010] An object of the invention is to provide a process for thermalcontrol of a plurality of separate components that can be accomplishedby a single TEC assembly.

[0011] Another object of the present invention is to provide a processfor thermal control that minimizes the risk of potential failure.

[0012] And yet another object of the present invention is to provide aTEC the configuration of which has a consistent optical centerline.

[0013] Another object of the invention is to provide for reducedassembly time, reduced cost, and increased quality and reliability of aTEC.

[0014] Other objects, advantages, and novel features of the presentinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the accompanyingdrawings and the following detailed description, in which like referencenumerals refer to like parts and where:

BRIEF DESCRIPTION OF THE FIGURES

[0015]FIG. 1 is a schematic diagram of a one thermal element circuit.

[0016]FIG. 2 is a schematic diagram of a one thermal couple circuit.

[0017]FIG. 3 is a schematic diagram of many thermal couples assembledtogether to form a thermoelectric cooler.

[0018]FIG. 4 is a schematic of a twin-TEC in accordance with the presentinvention including a bifurcated cold side ceramic plate.

[0019]FIG. 5 is at top down view of an optoelectronic package containinglaser, lens, and locker and the twin TEC.

[0020]FIG. 6. Relationship between Etalon angular misalignment andtemperature adjustment.

DETAILED DESCRIPTION

[0021] The conflict between thermal requirements and optical alignmentneeds prompted the current inventors to propose a twin-TEC 10, shown inFIGS. 3 and 4. Two partial circuits 12, 14 can be patterned andmetallized on upper and lower plates or more generally heat dissipatingand heat gathering plates, 16 and 18 respectively. The plates 16 and 18are preferably formed from ceramic, although other materials, known tothose skilled in the art may be used, including various thermalconductors that are not electrically conducting. After placing andsoldering a plurality of thermal couples between the plates, a superthermoelectric cooler with two complete sets of TEC is made. By removinga strip of ceramic from the top plate by cutting, slicing, etching, or avariety of other means for removing a portion of the heat dissipatingplate 16, a twin-TEC 10 is formed.

[0022] Since the twin-TEC 10 is initially built as one part, the twoseparate coolers, or cooling circuits 15, 17 have substantiallyidentical heights. The two separate circuits 15, 17 allow components oneach of them to be regulated somewhat independently.

[0023] People familiar with the art understand that TEC manufacturing isa manually intensive process. The process starts with plates 16, 18 thathave partial circuits 30 formed with metallization traces (patterns orart-works). N-type 20 and P-type 22 elements, which appear identical tothe eyes, are placed at their respective correct locations and areattached to the bottom plate by soldering, epoxying or some other methodwell-known to those skilled in the art. Each of the N-type elements 20have a top surface 31 and a bottom surface 27. Each of the P-typeelements 22 have a top surface 29 and a bottom surface 25. Traces on thetop plate 16 are matched and soldered to the top surfaces 29, 31 of eachof the elements 20, 22 that are to be in electrical communication withanother element 20, 22. Traces on the bottom plate 18 are matched andsoldered to the bottom surfaces 25, 27 of each of the elements 20, 22that are to be in electrical communication with a corresponding element20, 22. It is generally understood by those in the art that acorresponding element for an N-type 20 element is a P-type element 22and vice versa.

[0024] Terminal leads 32 or posts are then bonded, generally bysoldering, epoxying or some other well-known method, typically on thebottom plate, to complete the TEC circuit. Solder alloys can bepre-deposited on top and bottom surfaces of TEC.

[0025] Thick and thin film technologies have adequate lateral precisionand tolerance for making traces in the partial circuits patterned on theupper and lower ceramic plates 16, 18. The choice of one technology overthe other comes from process capability, material compatibility, andcost considerations. Thick film processes can be used on aluminum oxideceramics, while thin film technology is used on aluminum nitridematerials.

[0026] Placing and soldering elements to the bottom ceramic plate isprobably the most tedious process step in making of TEC. Using twin-TECdesign and manufacturing concept illustrated in FIG. 4, complexity levelof making the twin-TEC 10 remains the same as that of making regularTEC. The height of the twin-TEC 10 is always consistent. Obviously,there is no limit of the number of TECs that can be constructed as onepiece using this technique. Therefore, a plurality of TEC circuits maybe formed, thus creating a multi-TEC assembly.

[0027] In application, when temperatures of each of the TECs in amulti-TEC assembly are not too far apart, thermal interaction of themulti-TEC is negligible i.e., each of the coolers function substantiallyindependent from each other. For optoelectronic applications, thisimplies that components on the two TEC can be maintained at temperaturesof up to about 50° C. apart, which is very significant for manyapplications.

[0028] Take a simplified optoelectronic package 45 with laser 50, lens60, and internal locker 70 as an example. A top-down plan view of such apackage 45 is shown in FIG. 5. The laser 50 and lens 60 are attached toTEC1 80. The lens 60 collimates light emitted from the laser 50. Thelocker 70, which contains a beam splitter 72, two photo-detectors 74,such as PINs or APDs, or some other well known photo detector and anEtalon 76, is attached to TEC2 82. The two beam splitting surfaces tap asmall percentage of light into the photodetector 74. The first beam isfor reference, the second beam passes through the Etalon 76 and reachesthe second photodetector with a phase shift for wavelength-lockingpurposes.

[0029] Phase change, Φ, through Etalon is described by equation (1)$\begin{matrix}{\Phi = \frac{4\pi \quad {nL}\quad \cos \quad \theta}{\lambda}} & (1)\end{matrix}$

[0030] where X is wavelength of light, n is the index of refraction ofthe material between the mirrors, L is the distance between the mirrors,and θ is the incident angle of light beam.

[0031] Ideally, θ should be zero. In manufacturing, the Etalon willalways deviate from its ideal position. Typical incident angle to Etalonsurfaces, θ, ranges from 0.5 to 1.0° at three times standard deviation.

[0032] Temperature tuning becomes a powerful tool to compensate Etalonmisalignment. From equation (1), one finds phase change as a function oftemperature, T, as $\begin{matrix}{\frac{\Phi}{T} = {\frac{4{\pi cos}\quad \theta}{\lambda}\left( {{L\frac{\partial n}{\partial T}} + {n\frac{\partial L}{\partial T}}} \right)}} & (2)\end{matrix}$

[0033] ignore the less sensitive term,${n\frac{\partial L}{\partial T}},$

[0034] and rearrange, the relationship between incident angle andtemperature change is $\begin{matrix}{{\Delta \quad T} = \frac{n\left( {\frac{1}{\cos \quad \theta} - 1} \right)}{\frac{n}{T}}} & (3)\end{matrix}$

[0035] Knowing optical properties of an Etalon material, one cancalculate the temperature change needed to compensate a certain angularmisalignment. For fused silica, n=1.44,${\frac{n}{T} = {1.16 \times 0^{- 5}}},$

[0036] the relationship between angular misalignment of fused silicaEtalon and temperature change is depicted in FIG. 6. To compensate a 1°Etalon misalignment, one can heat the Etalon by 19° C. using TEC2 aboveroom (or reference) temperature.

[0037] The arrangement shown in FIG. 5 can also be used for tuning anEtalon to lock on different wavelength if the laser is tunable.

[0038] The foregoing description of a preferred embodiment of theinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in this art. Itis intended that the scope of the invention be defined by the followingclaims and their equivalents.

What is claimed is:
 1. A dual-TEC comprising: a heat dissipating plate;a heat gathering plate; a plurality of elements extending between andabutting each of the heat dissipating and heat gathering plates; aplurality of electrical connectors, each of said plurality of connectorsextending between at least an adjacent two of the elements; and whereinthe heat dissipating plate further includes an aperture extendingtherethrough.
 2. The dual-TEC of claim 1 wherein the plurality ofelements comprise N-type elements.
 3. The dual-TEC of claim 1 whereinthe plurality of elements comprise P-type elements.
 4. The dual-TEC ofclaim 3 wherein the plurality of elements further comp rise N-typeelements.
 5. The dual-TEC of claim 4 further comprising a plurality ofterminal leads.
 6. The dual-TEC of claim 1 wherein said plurality ofelectrical connectors comprise metallizations traces.
 7. The dual-TEC ofclaim 3 wherein said plurality of electrical connectors comprisemetallizations traces.
 8. The dual-TEC of claim 4 wherein said pluralityof electrical connectors comprise metallizations traces.
 9. The dual-TECof claim 5 wherein said plurality of electrical connectors comprisemetallizations traces.
 10. The dual-TEC of claim 1 wherein said heatdissipating plate is formed from ceramic.
 11. The dual-TEC of claim 7wherein said heat dissipating plate is formed from ceramic.
 12. Thedual-TEC of claim 8 wherein said heat dissipating plate is formed fromceramic.
 13. The dual-TEC of claim 9 wherein said heat dissipating plateis formed from ceramic.
 14. A dual-TEC laser assembly comprising: alaser diode; a heat dissipating plate; a heat gathering plate in thermalcommunication with said laser diode; a plurality of elements extendingbetween and abutting each of the heat dissipating and heat gatheringplates; a plurality of electrical connectors, each of said plurality ofconnectors extending between at least an adjacent two of the elements;and wherein the heat dissipating plate further includes an apertureextending therethrough.
 15. The dual-TEC of claim 14 wherein saidaperture extending through the heat dissipating plate forms two separateTECs.